1. Field of the Invention
The present invention relates to a method for recovery of polymer from polarizing plates, and to a method for producing recycled polymer films and polarizing plates employing recycled polymers.
2. Related Art
Polarizing plates are used in image display devices such as liquid-crystal display devices. As a polarizing plate, much used are those comprising a polarizing element of a polyvinyl alcohol film or the like dyed with a dichroic dye such as iodine, in which a transparent protective film, triacetyl acetate (TAC) film is stuck to one or both surfaces of the element. The polarizing plate is generally produced as a long film, and then cut into a predetermined size and used in liquid-crystal display devices, etc. However, depending on the required dimensions or directions of absorption axes thereof, the area yield of polarizing plates are poor, which generates a problem in that the production process gives a large quantity of industrial wastes.
For example, for recovery of polymer that is a material of protective film from polarizing plate, there are known a method of recovery of a cellulose ester by processing a polarizing plate with water (Japanese Laid-Open Patent Publication No. 2001-181440), and a method of production of a recycled TAC film, comprising processing a polarizing plate having a TAC film as a protective film with a solvent to give a TAC solution, and forming a film from the solution (Japanese Laid-Open Patent Publication No. 2003-195048).
On the other hand, with the recent requirement for high-quality and thin-body liquid-crystal displays, the polarizing plate to be used in them is also required to have a bettered quality; and for the purpose of producing such a high-quality polarizing plate, a film that differs from a TAC film or the like cellulose ester film in the physical and chemical properties thereof has become used as a protective film for the polarizing plate. For example, as an example thereof having improved durability, there is proposed a polarizing plate that comprises a film having a smaller moisture permeability than a TAC film as one protective film therein.
As above, conventional polarizing plates generally have the same protective film on both surfaces of the polarizing element therein; recently, however, a polarizing plate in which both surfaces of the polarizing element are asymmetrically protected with different protective films are being put into practical use, for which, therefore, a recycling method is necessary that comprises separately recovering the different protective films from the thus-constructed polarizing plate. However, when the asymmetric polarizing plate of the type is processed according to the above-mentioned recovery method heretofore proposed, then the protective films stuck to both surfaces of the polarizing element may be mixed during the processing procedure, and therefore they could not be recovered separately. For example, when the protective films are dissolved in a predetermined solvent according to the method described in the above mentioned Japanese Laid-Open Patent Publication No. 2003-195048, then the materials of the protective films may mix together therefore resulting in that both the recovered materials are much contaminated with impurities. On the other hand, when the protective films are peeled away from the polarizing element through processing with water according to the method described in the above mentioned Japanese Laid-Open Patent Publication No. 2001-181440, there also occurs a problem in that the protective films mix together. Naturally, for recovered and recycled materials, it is desirable that the impurities therein are minimized as much as possible.